Baha Mousa was 26 when he died. A recent widower, following the death of his young wife from cancer, he looked after his three- and five-year-old sons and worked at a hotel in Basra. Over the course of three days last September, according to eyewitnesses, he and six other hotel employees were systematically beaten, abused, humiliated and tortured while detained by members of the Queen's Lancashire Regiment. The treatment was sanctioned by at least one officer.

Their crime, it seems, was to work for the owner of the hotel, a man called Haitham, who had hidden guns in the building. Those responsible for the torture assumed (wrongly) that the men knew where Haitham was hiding.

Baha died three days later in custody. The death certificate variously records the cause as "cardio-respiratory arrest" and "asphyxia". Evidence from the other witnesses describes systematic abuse including a kickboxing ritual where soldiers competed to see how far they could throw a detainee with their kicks. Kifah Taha Al-Mutari, aged 44, one of the detainees, developed an acute kidney problem and others suffered broken ribs, concussion, difficulty in breathing and various other injuries. Was this an isolated incident involving rogue elements within a single regiment?

I am a solicitor acting in the cases of 20 Iraqis killed or injured by British troops during the occupation. Their stories, often substantiated by letters from the British military, depict culpability of many regiments over a period of months. All suggest that, were the truth revealed by an independent inquiry, it would have dramatic implications for the accountability of the Ministry of Defence. It would also involve those high up the chain of command, including in government, who knew or should have known that something went terribly wrong during Britain's occupation of Iraq. The evidence suggests that those responsible for the decision to go to war, and for the subsequent occupation, simply failed to plan properly, or at all, for the inevitable; namely, that the Iraqi population would not quietly accept the brutality of war and occupation. That brutality included the deliberate use of indiscriminate weapon systems, such as cluster bombs, in urban areas.

Let us not forget the other cases. One man was killed when British troops burst into his home as he prepared for morning prayers. Another was shot while repairing a pump on his farm. A woman was shot during an evening supper with her family. A policeman was shot on the street delivering papers to a judge. Two men were killed by mistake when guns were discharged, as is the local custom, at a funeral. None of the cases suggest troops gave warnings in accordance with rules of engagement or fired in self-defence. At best, terrible mistakes have been made - and many of them, bearing in mind the written answer of armed forces minister Adam Ingram on May 28 that the government admits to 10 deaths in detention. At worst, British troops, and those who command them, can kill with impunity because there is no effective mechanism for accountability within domestic or international law.

There are those who seek to detract from the harsh realities of these cases. War, they say, has unfortunate consequences for civilians. But these incidents arise from a period after the official cessation of hostilities when Britain was in effective control of south-east Iraq, having assumed the functions of the local state, police, judiciary and legislature. Instead, these people turn their focus on to the lawyers who are portrayed as "ambulance-chasing" and "poison-tongued" for suggesting that unlawful killings must be subject to an independent inquiry, and that full accountability must include proper compensation.

The government's legal case is crystal clear. It says that there will not be an independent inquiry or military investigation into the deaths. This is because, on its case, a legal black hole exists. The military can abuse, humiliate, degrade, torture and even kill Iraqi detainees, or other civilians conducting their lawful business on their own property, without being bound by the Human Rights Act, which the present government introduced in 1998. Unless an internal military investigation decides to court-martial an individual soldier, the relatives of those killed are left with nothing. I have been kept completely in the dark. Although there are, according to the national press, criminal investigations underway into at least the death of Baha Mousa, nobody has written to me on behalf of my clients asking for information or offering reassurance or an apology.

Under the regulations passed by the Coalition Provisional Authority, there is immunity for these acts under Iraqi law. The US and Britain want immunity to continue after June 30, putting emphasis on domestic accountability where, in practice, there is none. If this legal analysis prevails, principles of democracy and the rule of law count for little in post-occupation Iraq.

On the other hand, the claimant families argue for full legal accountability. On July 28-30, in a high court test case, it will be argued that the European convention on human rights (ECHR), and the Human Rights Act which gives it effect in UK law, applies because Britain is in effective control of south-east Iraq. Accordingly, there must be an independent inquiry as required by numerous Strasbourg cases, many arising from the shoot-to-kill policy in Northern Ireland. If the inquiry finds these were unlawful killings, full compensation must be paid. Further, there must be prosecutions of those responsible for war crimes, no matter how high up the chain of military and political command. Britain is bound by the international criminal court (ICC) and if the attorney general refuses prosecutions, the cases will be referred to the ICC prosecutor.

The question of whether the ECHR applies to British armed forces in south-east Iraq has important consequences for future conflicts and peacekeeping operations. In future, the state would be bound to hold independent inquiries into incidents of torture and killings, once effective control of another state's territory was established. The principle would bind all signatories to the ECHR, including the European members of Nato. It should be impossible for a future government to escape with impunity if it signs up to a war alongside the US. While the US continues to assert that the ICC has no jurisdiction over it, its partners would be accountable under the principle of joint and several liability. Those making a decision to go to war would be bound to ensure that every member of the British armed forces is fully aware of the consequences of human rights violations. If the prison service in the UK cannot escape with impunity if a prisoner dies after ill treatment, or if police officers on the streets of Birmingham are not permitted to shoot and fatally wound unarmed citizens, why should there be a completely different regime if Britain is in occupation of another territory? Basic principles of justice and the operation of the rule of law dictate that this legal black hole, prised open after 9/11 by both the US and Britain, must now be closed. Otherwise, this current international lawlessness can only lead to a dramatic counterattack by those on the receiving end of this new world order.